The invention concerns a system for the suspension and hoisting of a load support.
There is known one type of a device for the suspension and hoisting of a load support, such as a work nacelle, wherein the support is suspended by four suspension reaches constituted in total by only at least two suspension elements, such as cables or ropes, each extending down from a fixed point located above one of the opposite ends of the load support, and reeved around circular rotatable deflection supports, such as pulleys, located adjacent the two ends of the load support, and to be connected each to a lifting means, such as a winch, located above the other end of the load support. These circular supports are arranged to be in integral rotation with the suspension elements which they are associated. The circular supports must not be disposed at the ends of the load support but need only be spaced at equal distances from the center of the load support towards the opposite ends thereof, without thereby changing the desired effect. In general, it is recommended for the suspension reaches of such a device to be disposed vertically, but the suspension device may also have oblique suspension reaches. Additionally, it is pointed out that the center of gravity (G) of the load support should be located below the transverse reaches of the cables or ropes joining the pulleys so as to insure the support to be stable in transverse direction. This known system has the advantage of requiring only two lifting means or hoists for four suspension reaches. The FIG. 1 is a schematic illustration of such a known device.
The device as described previously has the disadvantage of providing a load support which will incline longitudinally towards the side of the load by rolling movement of the pulleys on the cables or ropes when the load displaces from the axis of gravity Ag of the support towards one of the load support ends. For example, as soon as a user standing on a support, constituted by a nacelle, which is initially in horizontal position, moves away from the center thereof towards the one or the other end of the nacelle, the nacelle will assume a position inclined towards the same side. The inclination increases until the bottom of the nacelle approaches a position aligned with the suspension reach of the cable or rope located on the side opposite from the side towards which the load is displaced, as shown in FIG. 2. In practice, in the case of the load support being a nacelle, this movement is limited, without being eliminated, by the guiding of the suspension reaches, by means of vertical extensions of the nacelle, such as stirrups. Such a movement limited as referred to above is shown in FIG. 3.